US3375185A

US3375185A - Anode for alumina reduction cells

Info

Publication number: US3375185A
Application number: US383370A
Authority: US
Inventors: Robert M Kibby
Original assignee: Reynolds Metals Co
Current assignee: Reynolds Metals Co
Priority date: 1964-07-17
Filing date: 1964-07-17
Publication date: 1968-03-26
Anticipated expiration: 1985-03-26
Also published as: GB1086135A

Description

March 26, 1968 Filed July 17. 1964 R. M. KIBBY I 3,375,185

ANODE FOR ALUMINA REDUCTION CELLS 5 Sheets-Sheet 1 INVENTOR.

ROBERT M. KIBBY f BY ` Afro/wg March 26, 1968 R. M. KlBBY 3,375,185

' v ANODE FOR ALUMINA REDUCTION CELLS Filed July 17, 1964 5 Sheets-Sheet 2 INVENTOR.

ROBERT M. KIBBY MBY;

ATTORN 3.

March 26, 1968 `R. M. KIBBY 3,375,185

ANODE FOR ALUMINA REDUCTION CELLS Filed July 1v, 1964 5 sheets-sneer f Ill...

INVENTOR.

ROBERT M. KIBBY BY A March 26, 1968 R. M. KIBBY ANODE FOR ALUMINA REDUCTION CELLS 5 Sheets-Sheet 4 Filed July 17, 1964 INVENTOR.

ROBERT M, KIBBY ATTRNY..

March 26, 1968 R. M. KIBBY ANODE FOR ALUMINA REDUCTION lCELLS 5 Sheets-Sheet i) Filed July 17, 1964 INVENTOR. ROBERT M. KIBBY ATTO/i E YS.

United States Patent() 3,375,185 ANUDE FR ALUMHNA REDUCTION CELLS Robert M. Kibby, Florence, Ala., assignor to Reynolds Metals Company, `Richmond, Va.,` a corporation of Delaware Filed July 17, 1964, Ser.' No. 383,370 6 Claims. (Cl. 204-280) ABSTRACT F THE DISCLOSURE The anode for alumina reduction cells comprises a pack of vertically disposed prebaked carbon slabs including electrical contact members extending into spaces `between the slabs. In a preferred em-bodiment adjacent faces of the slabs are formed with opposed elongate recesses into which the Contact pins extend to key adjacent slabs together against relative movement, and in another embodiment the slabs are .spaced apart from one another, the Contact members being at bars extending inwardly between slabs. Carbon paste between the slabs surrounds the contact `members, holding them in place forming an integral structure. As the paste is consumed somewhat more rapidly than the slabs, channels are created to assist in removing gas, with the lowermost contact members being removed from time-to-time as the anode is consumed, thus creating preformed gas channels to relieve the shrouding effect of the gas.

SUMMARY According to my invention, an anode comprising a pack of vertically disposed prebaked carbon slabs includes electrical contact members (metal pins) extending into spaces between the slabs. yThese contact members are arranged for selective withdrawal from the spaces between the slabs, the lowermost pins being pulled out as the anode burns away at the bottom and is progressively lowered into the molten electrolyte during .use of the anode in the electrolytic cell. Anelectrically conductive cementitious substance such as a carbon paste disposed between the slabs holds the pins in place in the spaces between the slabs. In a preferred embodiment of my invention, the slabs have their adjacent faces formed with opposed elongate recesses into which the contact pins extend in a manner that serves to key adjacent slabs together against relative movement. In another embodiment, contact pins in the form of flat metal bars extend inwardly from the vertical side edges of the slabs to be received in the spaces between the flat unrecessed faces of adjacent slabs, the slabs being spaced apart from one another. In this case the carbon paste, in filling the spaces between the slabs, surrounds the pins. In both cases the paste holds the contact members in place lbetween the slabs, forming an integral structure.

Because the pins, which extend inwardly from the vertical side edges of the slabs, are lalso disposed between the slabs, withdrawal of the lowermost pins serves to create preformed gas channels which assist in releasing gas bubbles produced at the lower active surfaces of the anode. As the carbon paste between the slabs is consumed by burning away somewhat more rapidly than the carbon of the slabs, the gas channels left by the burnedout paste will be in open communication with the firstmentioned preformed gas channels created by withdrawal of the lowermost pins. Thus, the locating of the pins between the slabs, by creating preformed gas channels, assists in relieving the action surfaces of the anode from the shrouding. effect of the gas, accomplishing a quieter and more uniform gas release. Further, this manner of locating and attaching the pins to the anode pack cornbines in a single structure the advantages of a prebaked 3,375,185 Patented Mar. 26, 1968 ICC slab anode from the standpoint of ease of renewal and good heat dissipation with those of the well-known Soderberg. anode from the standpoint of continuous operation and simplicity of interchange of electrical connectors as Vthe anode is used up.

According to another feature of my invention, the pack of slabs is held between opposed series of horizontal frame members extending across the vertical side edges of the slabs. These frame members have openings to receive the contact pins. In this construction the frame members serve to restrain the carbon paste from seeping out between the side edges of the slabs as the paste flows into the spaces between the slabs; and because the contact pins can engage the edges of the openings in the fr-ame members, such members serve also to transmit lifting forces between the slabs and the frame members.

These and other features and advantages of my anode construction will appear more fully as the description proceeds.

DESCRIPTION With reference to the laccompanying drawings, I shall now describe the best mode contemplated by me for cartying out my invention.

FIG. 1 is a perspective view of an anode constructed in accordance with my invention, shown in its relationship to a preheating platform used in starting the forma- .tion of the anode.

FIG, .2 is a side elevational View partly in vertical longitudinal section showing the same anode construction in use in an electrolytic -cell for the production of aluminum.

FIG. 3 is an end elevational view, partly in vertical transverse section, of the structure of FIG. 2.

FIG. 4 is an enlarged detail view showing, in vertical transverse cross section through the space between two adjacent slabs, a portion of the lower end of the anode of FIGS. 2 and 3.

FIG. 5 is a detail side elevational view taken as indicated at 5-5 in FIG. 4.

FIG. 6 is a detail side elevational view similar to FIG. 5 showing a modified form of my invention.

FIG. 7 is a vertical transverse sectional view taken on the line 7-7 of FIG. 6.

-THE ANODE PACK As shown in FIG. 1, my anode comprises a pack of vertically disposed prebaked slabs 1, 2 and 3 (and multiples thereof) advantageously formed of carbon. Electrical contact members, here shown in the form of round metal pins 4, extend into spaces between the slabs, these pins being connected to a source of electric power such as the busbar 5 (FIGS. 2 and 3) by electrical connectors 6, generally termed llexibles The contact members 4 are arranged for selective withdrawal and insertion from and into the spaces between slabs, the lowermostpins being pulled out as the anode burns away at the bottom vand is progressively lowered into the molten electrolyte 7 during use of the anode in the electrolytic cell 8. A cementitious substance such as a carbon anode paste 10 of a typically Soderberg compositiondisposed between the

slabs

1, 2, 3, etc., holds the pins in place in the spaces between the slabs.

In my preferred construction illustrated in FIGS. l to 5, inclusive, the slabs have their adjacent faces formed with opposed elongate recesses 9 (see FIGS. 3 and 4) into which the contact pins 4 extend in a manner that serves to key adjacent slabs together against relative vertical movement. Because thepins 4, which extend inwardly from the vertical side edges of the

slabs

1, 2, 3, are also disposed between the slabs, withdrawal of the lowermost pins serves to create preformed gas channels 11,

3 FIGS. 4 and 5, which assist in releasing the gas bubbles produced at the lower active surfaces of the anode. As the carbon pitch of the pastel between the slabs is consumed by burning away somewhat more rapidly than the carbon of the slabs, the gas channels 12 (FIG. 5) left by the burned-out paste 10 will be in open communication with the first-mentioned preformed gas channels 11 created by withdrawal of the lowermost pins 4. Thus the locating of the pins between the slabs, by creating preformed gas channels, assists in relieving the ac tive surfaces of the anode from the shrouding eect of the gas, accomplishing a quieter and more uniform gas release. The opposed elongate recesses 9 extending inwardly from the vertical side edges of the slabs advantageously are inclined upwardly and outwardly to conduct the gasses upwardly and outwardly to the side edges of the slabs for release at the sides of the pack.

The pack of slabs is held between the opposed series of horizontal frame members 13 conveniently consisting of channel irons. These frame members extend across the vertical side edges of the slabs and since they are arranged in abutting relationship, as will be understood from FIGS. 4 and 5, they together form an inner wall surface serving to restrain the carbon paste, when flowed into spaces 14 between the slabs, from seeping out between the side edges of the slabs. Frame members 13 have openings 15 to receive contact members 4, such contact members thereby serving also to transmit lifting forces between the slabs and the frame members by supporting means to be described.

FIGS. 6 and 7 illustrate another embodiment of my in- Vention in which contact pins in the form of at metal bars 16 extend inwardly from the vertical side edges of the slabs to be received in the spaces 14 between the ilat unrecessed faces of adjacent slabs. The carbon paste 10 in filling the spaces between the slabs surrounds the pins. In this embodiment as in the embodiment of FIGS. l-5, the paste holds the contact members in place between the slabs, forming an integral structure. Frame members 13 correspond to the frame members 13 of the previous embodiment except that the openings 15 for the pins will be rectangular instead of round.

The frame members 13 or 13', in addition to the functions already described, form a part of the means for clamping the slabs together during formation and use of the anode. Tie rods 17, extending through openings near the ends of the opposed frame members, pull them together against the side edges of the slabs. If desired, plates 13 may be inserted between the tie rods 17 and the end surfaces of the pack of slabs to complete a box-like frame. Lugs 19 fixed to the ends of the frame members provide means for attaching the anode frame to anode hangers 20 attached to supportings cables 21 of a suitable anode suspension and its operating means 22. The anode suspension and operating means may be of any wellknown construction such as commonly employed today in the suspension of Soderberg-type electrodes, utilizing a typical supporting fram-e indicated generally by the reference 23. In addition to the anode hangers 20 arranged at the four corners of the anode there should be provided a set of temporary hangers 24 used to support the anode during relocation of the hangers 20 as will be described. Temporary hangers 24 are supported from frame 23 as at 25; are provided with hooks 26 engaging openings 27 in brackets 28 fixed to frame members 13. The lower ends of the temporary hangers 24 advantageously include a flexible section 29 such as the chain shown, and a turnbuckle 30 furnishes means for adjustment to the right length during use.

It is of advantage to make the starting

slabs

1, 2 and 3 of different lengths so that, as the anode is burned up during use, fresh slabs added at the top of the pack will be offset from one another with the joints between them staggered. Once the pack has been started, the added slabs can all be of one standard length.

4 STARTING THE ANODE One method of building up a starting anode structure is illustrated in FIG. l, in which the starting

slabs

1, 2, 3, etc., are assembled in a thin sheet steel pan 31 resting on a bed of coke 32 on a steel platform 33. The sides of the pan 31 extend up to meet the edges of the lower set of frame members 13. For proper and uniform separation of the slabs, thin wafers of carbon (not shown) may be placed between them at appropriate spaced locations. Thus properly spaced, the nuts at the ends of the tie bars 17 are tightened to clamp the assembly together. The slabs may, for example, be on the order of six inches thick, ve feet wide and for the longest slabs, nine feet high. When supported in spaced relationship in the manner described, the spaces between them are filled with bonding paste 1t) up to the level of the uppermost frame members 13 as shown at 10' in FIGS. 4 and 5. After the paste has wet the surfaces of the slabs, the current collector pins 4 are inserted into the soft paste. The lanode is then heated by `passing electric current from the pins 4 to the bottom of the slabs until the paste has been baked. Coke packed around the pan 31 burns and contributes to heat for baking the paste. The initial anode current connections can be made to the slabs through the flexibles 6 and by means of connectors 34 joining the platform 33 to bus 35. Alternatively, in a new pot coke can be spread upon the pot bottom and a pan of light gauge sheet steel placed upon this layer of coke, anode bus connections being made as before. The pan, being of light gauge sheet steel, is destroyed in the initial baking operation. The pan and the frame members serve to keep the paste from owing out the bottom or the sides while the paste is being baked out to form a mass of carbon in the region of the lower frame members and below. The prebaked slabs will be finished at around l,200 C., but the pitch coke of the paste will not normally be baked out at above 1,000 C. (pot temperature). The result is that the overvoltage on the pitch coke of the paste will be lower than on the baked slabs. The current will concentrate in the line vof least resistance, producing greater electrical activity on the pitch carbon until such time as the increased travel through the bath offsets the difference in overvoltage. The carbon between the slabs will therefore be preferentially consumed, generating the gas release slots 12 as previously described.

OPERATION As the electrode burns away at the bottom it is gradually lowered into the electrolyte 7. When the lowermost frame members 13 reach a point near the top of the bath or the crust which overlies it, flexibles 6 are disconnected from the lowermost set of pins 4 and reconnected to the next higher set of pins, temporary hangers 24 are connected to the next higher set of frame members 13, operating hangers 20 disconnected from the lugs 19 of the lowermost set of frame members and connected to the lugs of the next higher set. Next the lowermost set of frame members 13 is unbolted and removed, this set of frame members then being reassembled above the uppermost set of frame members 13. 'In like manner the other frame members are in turn stripped from the bottom of the anode and added to the assembly higher up, additional paste being added at the top and the pins removed from below being reinserted in the new position. As each set of lowermost pins 4 is removed, a new series of gas relief channels 11 is formed. As needed, additional slabs are added at the top of the anode, rst placing a layer of carbon paste, as at 36, over the top of the slab below as shown in FIG. 5.

The terms and expressions which I have employed are used in a descriptive and not a limiting sense, and I have no intention of excluding equivalents of the invention described and claimed.

I claim:

1. An anode for electrolytic cells for the production of aluminum, comprising a pack of vertically disposed prebaked slabs, said slabs having adjacent faces formed with opposed elongate recesses and contact members extending into said opposed elongate recesses and serving to key adjacent slabs together against relative movement, electrical connectors for connecting said contact members to a source of electrical power, said contact members being arranged for selective withdrawal from the spaces between the slabs, and an electrically conductive cementitious substance disposed between the slabs and holding the contact members in place in the spaces between the slabs.

2. An anode constructed in accordance with claim 1 in which said opposed elongate recesses extending inwardly from the vertical side edges of the slabs, whereby upon withdrawal of the lowermost contact members gas channels 4are formed between the slabs by said opposed elongate recesses from which said lowermost contact members have been removed.

3. An anode constructed in accordance with claim 1 in which said opposed elongate recesses extending inwardly from the vertical side edges of the slabs, whereby upon withdrawal of the lowermost contact members gas channels are formed between the slabs by said opposed elongate recesses from which said lowermost contact members have been removed, said inwardly extending opposed elongate recesses being inclined upwardly and outwardly to conduct gases upwardly and outwardly to the side edges of the slabs for release at the sides of the pack.

4. An anode constructed in accordance with claim 1 in which the pack of slabs is held between opposed series of horizontal frame members extending across the vertical side edges of the slabs, said frame members serving to restrain the cementitious material when flowed into spaces between the slabs from seeping out between the side edges of the slabs, and said frame members having openings 4to receive said contact members, said contact members thereby serving also to transmit lifting forces between the slabs and the frame members.

5. An anode for electrolytic cells for the production of aluminum, comprising a pack of vertically disposed prebaked slabs, said slabs being spaced apart from one another, electrical contact members extending into spaces between the slabs, said contact members being flat bars having portions extending inwardly into the spaces between the slabs, electrical connectors for connecting said contact members to a source of electrical power, said contact members being arranged for selective withdrawal from the spaces between the slabs, and an electrically conductive Icementitious substance disposed between the slabs and holding the contact members in place in spaces between the slabs, said cementitious substance surrounding the inwardly extending portions of the flat bars and filling the spaces between the slabs.

6. An anode constructed in accordance with claim 5 in which the pack of slabs is held between opposed series of horizontal frame members extending across the vertical side edges of the slabs, said frame members serving to restrain the cementitious material when flowed into spaces between the slabs from seeping out between the side edges of the slabs, and said frame members having openings to receive said contact members, said contact members thereby serving also to transmit lifting forces between the slabs and the frame members.

References Cited UNITED STATES PATENTS 2,739,113 3/ 1956 Horsfield et al. 204-243 2,822,328 2/ 1958 Walker 204-247 3,052,619 9/ 1962 Schmitt 204-288 XR FOREIGN PATENTS 689,368 6/ 1964 Canada.

HOWARD S. WILLIAMS, Primary Examiner.

D. R. I ORDAN, Assistant Examiner.